Knowledge as a key determinant of public support for autonomous vehicles

Autonomous vehicles (AVs) have the potential to revolutionize transportation safety and mobility, but many people are still concerned about the safety of AVs and hesitate to use them. Here we survey 4112 individuals to explore the relationship between knowledge and public support for AVs. We find that AV support has a positive relationship with scientific literacy (objective knowledge about science) and perceived understanding of AV (self-assessed knowledge). Respondents who are supportive of AVs tended to have more objective AV knowledge (objective knowledge about AVs). Moreover, the results of further experiments show that increasing people's self-assessed knowledge or gaining additional objective AV knowledge may contribute to increasing their AV support. These findings therefore improve the understanding of the relationship between public knowledge levels and AV support, enabling policy-makers to develop better strategies for raising AV support, specifically, by considering the role of knowledge, which in turn may influence public behavioural intentions and lead to higher levels of AV acceptance.


Materials and Methods
Note S1.Full informational text materials of Studies 1 and. 2 Note S2.Full informational text materials of Study 3a Note S3.Full informational text materials of Study 3b Table S1.Sample details for different studies Table S2.Analysis of linear regression by study Table S3.The difference of objective knowledge by different levels of support in Study 2a and Study 2b Table S4.Sensitivity analysis.Regression analysis of public support and scientific literacy after removing the AV question from the "scientific literacy" scale References

Instrument development
The scientific literacy (objective knowledge about science) measure construction in Study1 is adopted from previous research about scientific knowledge 1,2 , which is widely used in surveys of public knowledge in various countries 3,4 .The measure items are considered elementary nature, including the public's knowledge of physics and earth sciences(5 items), astronomy(2 items), biologic sciences and human origins(2 items), health care(3 items), and AV(1 item).These 15 true-false questions measured respondents' scientific literacy score, which was calculated as a total score based on the results of their answers (1 point for the correct answer, 0 points for the wrong answer, or "Do not know").Having a high level of scientific literacy means having a good understanding of the process of scientific study, disciplinary constructs and some contemporary political issues 5 .Similar to other studies on scientific knowledge 6 , one item in the "scientific literacy" scale refer to our research topic(AV).For robustness, we also replicated the analyses after removing the AV question from the "scientific literacy" scale.The results of the sensitivity analysis are consistent with our reported conclusions, which indicates that our results are robust.Details are shown in Table S4.
Objective knowledge about AVs.The development of measures for the timely study of emerging phenomena such as automated vehicles do not always permit careful psychometric testing 11 , and there hasn't been a universally-acknowledged scientific paradigm measuring objective knowledge to date 10 .Therefore, with reference of the National Science Foundation's measure of the public's scientific literacy, we divide the measure of AV objective knowledge into three dimensions: understanding the definitions of AV (items 1-3), understanding AV-related concepts (e.g., terms such as degree of automation, connected vehicles, etc.) (items 4-7), and understanding of some public policy issues or social conditions that involve or directly affect AV (items 8-10).
Public support for AVs.The public support was measured by asking respondents what extent they support for AVs, ranging from "not support at all" to "very support" .This single measure was adapted from previous studies 2, [12][13][14][15] .We also tested the reliability of the construct of support, a 3-item survey with a Cronbach's alpha of α = 0.781.

Methods
The design of our questionnaire mainly includes the following steps: 1.To learn more comprehensively and profoundly about the relationship between individual knowledge and support for AVs, we identified the following main research points: 1) The relationship between public's self-assessed and objective knowledge and support for AVs; 2) The relationship between public's self-assessed and objective knowledge and willingness to ride and buy AVs; 3) The relationship between public's self-assessed and objective knowledge and the scenarios of different risk holders related to AVs; 4) Impact of changes in public's self-assessed or objective knowledge on support for AVs; 2. We tested and evaluated preliminary questionnaires on the Baidu Data Crowdsourcing Platform.
3. We adhered to the Baidu Data Crowdsourcing Platform's requirements and modified the four questionnaires' format and content, reducing each study's time to 5-10 minutes.
4. We divided the research into two parts: the online survey Study 1, 2, and 3b were completed through the Baidu Data Crowdsourcing Platform; Study 3a was completed through the experiment because it required researchers to provide respondents with feedback on their real knowledge scores.
After a brief experimental introduction, the respondents were asked whether they would accept and complete the survey.Subsequently, we first asked the respondents about their access to information about AVs and then explained the AVs (the explanation is based on SAE J3016's definition of Level 4 and Level 5 autonomous driving systems).
In all studies (N=4112), we collected data on the support for AVs (Study 1, Study 3a, Study 3b: support for AVs; Study 2a: support for AVs, willingness to ride and buy AVs; Study 2 b: support for AVs with the scenarios of different risk holders) and their self-assessed knowledge as well as objective knowledge measured by 10-15 questions.
Additional questions were to measure the change of respondents' self-assessed and objective knowledge in Study 3a and Study 3b.Questions about demographic information were at the end of each questionnaire.
Baidu Data Crowdsourcing Platform will provide remuneration for respondents who complete the questionnaire and collect their completion time and data results.The complete questionnaire content can be found in the supplementary materials.
Study 1 is aimed to explore the relationship between the public's self-assessed and general objective knowledge and their support for AVs.
First, we asked the respondents to evaluate their support for AVs ("1 = not support at all" and "5 = very support") and understanding (("1 = not understand at all" and "5 = understand very well") using a five-point Likert scale.After completing the assessment, we used 15 true-false questions to measure respondents' general objective knowledge score, which was calculated by the results of the answers (1 point for the correct answer, 0 points for the wrong answer, or "Do not know").These questions were derived from previous studies on the public's knowledge 1,3,16 , including a question about AVs 17 .These questions paved the way for further study of the public's objective knowledge of AVs in subsequent experiments.Finally, we asked the respondents about their basic personal information, including gender, age, income, education, purchasing, and driving experience.
Therefore, Study 2a aims to explore whether the public is willing to ride or buy AVs based on Study 1.
In addition to the "Support for AVs" section of the questionnaire, questions about riding willingness and purchasing willingness ("1 = certainly would not" and "7 = certainly would") were added based on Study 1.We also changed the original 15 questions about general objective knowledge to 10 questions related to AVs, which were adapted from previous studies in the field of AVs 5,[17][18][19] .
Study 2b used the form of "situation introduction" to ask respondents to substitute themselves into three different scenarios.The purpose is to explore the public's support for AVs from the scenario of varying risk holders.
Therefore, three scenarios were added to the part of "Support for AVs" in a questionnaire.Further, the respondents were asked about their support for AVs from these scenarios ("1 = not support at all" and "9 = very support").The descriptions of these scenarios are as follows: "Please imagine yourself riding in AVs in the future"; "Please imagine your relatives or friends riding in AVs in the future"; and "Please imagine AVs driving on the road in the future." Study 3a aims to explore how changes in respondents' self-assessed knowledge affects their support for AVs through experiments.
Similar to previous research, we first asked respondents to evaluate their support and understanding of AVs on a 100-point scale.The aim of measurement change is to analyze respondents' change of support and self-assessed understanding after self-assessed knowledge changes.Subsequently, we measured respondents' objective knowledge in the field of AVs using the same 10 questions as in Study 2.
We changed respondents' self-assessed knowledge by showing them their score in the objective knowledge test, reflecting their real self-assessed knowledge.After answering 10 truefalse questions about AVs' objective knowledge, the test score was provided to the respondents by the researchers.Subsequently, respondents were asked to evaluate how much they knew about AVs again.Finally, the respondents were asked to choose a value from 1-100 to assess their support for AVs and fill in the basic personal information.
In Study 3b, we used the same research strategy to explore how objective knowledge changes affected AVs' support.This study's process was similar to Study 3a, except that after collecting the initial data of respondents' knowledge and support, we changed the respondents' objective knowledge and collected the changes of support.Respondents were asked to read three paragraphs of text about AVs.Based on the results of previous research, the text was divided into three aspects: research history, concept, and definition, as well as relevant laws and regulations.After the reading, the respondents were asked to answer three questions based on what they had read, which was regarded as measuring whether their objective knowledge had changed.

Note S1. Full informational text materials of Studies 1 and 2 (i) Study 1 Survey Question
Introduction to Survey: This questionnaire will ask you about your knowledge and support for autonomous vehicles (hereafter referred to as AVs), and some information that is not personal privacy.The questionnaire is expected to take you 5-10 minutes.We would appreciate your participation.
If you do not have enough knowledge about the relevant content in the questionnaire, or this does not currently belong to your research field, it does not matter.We hope to get your real views and opinions, which will be very helpful for our research.

▪ Explanation of AVs:
AVs, also known as driverless vehicles, self-driving cars.It uses a driverless system to complete all driving operations, and human drivers can take over.▪ AVs Support Questions: "Please rate your level of support for AVs." ("1 = not support at all" and "5 = strongly support") ▪ AVs Self-assessed Knowledge Questions: "Please rate your understanding of AVs." ("1 = not understand at all" and "5 = understand very well") ▪ AVs Objective Knowledge Questions

The center of the Earth is very hot. (True, False, I don't know) 2. The continents have been moving their location for millions of years and will continue to move. (True, False, I don't know)
3. The earth orbits the sun.( This questionnaire will ask you about your knowledge and support for autonomous vehicles (hereafter referred to as AVs), and some information that is not personal privacy.The questionnaire is expected to take you 5-10 minutes.We would appreciate your participation.
If you do not have enough knowledge about the relevant content in the questionnaire, or this does not currently belong to your research field, it does not matter.We hope to get your real views and opinions, which will be very helpful for our research.▪ Explanation of AVs: AVs, also known as driverless vehicles, self-driving cars.It uses a driverless system to complete all driving operations, and human drivers can take over.▪ AVs Support Questions: "Please rate your level of support for AVs." ("1 = not support at all" and "7 = strongly support") "Are you willing to ride an AV?" ("1 = certainly would not" and "7 = certainly would ") "Are you willing to buy an AV?" ("1 = certainly would not" and "7 = certainly would ") ▪ AVs Self-assessed Knowledge Questions: "Please rate your understanding of AVs." ("1 = not understand at all" and "7 = understand very well") "Among the people I know, I can be regarded as an "expert" in the field of AVs." ("1 = strongly disagree" and "7 = strongly agree") "I know how to identify and pick AVs." ("1 = strongly disagree" and "7 = strongly agree") ▪ AVs Objective Knowledge Questions This questionnaire will ask you about your knowledge and support for autonomous vehicles (hereafter referred to as AVs), and some information that is not personal privacy.The questionnaire is expected to take you 5-10 minutes.We would appreciate your participation.
If you do not have enough knowledge about the relevant content in the questionnaire, or this does not currently belong to your research field, it does not matter.We hope to get your real views and opinions, which will be very helpful for our research.

▪ Explanation of AVs:
AVs, also known as driverless vehicles, self-driving cars.It uses a driverless system to complete all driving operations, and human drivers can take over.▪ AVs Support Questions: "Please rate your understanding of AVs." ("1 = not understand at all" and "9 = understand very well") "Among the people I know, I can be regarded as an "expert" in the field of AVs." ("1 = strongly disagree" and "9 = strongly agree") "I know how to identify and pick AVs." ("1 = strongly disagree" and "9 = strongly agree") ▪ AVs Objective Knowledge Questions: 1 The following survey is part of a research project carried out by State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, which is about your knowledge and support for autonomous vehicles (hereafter referred to as AVs), and some information that is not personal privacy Our research results will be used to explore public's attitude and behaviors towards the development of science and technology in the future.
If you do not have enough knowledge about the relevant content in the questionnaire, or this does not currently belong to your research field, it does not matter.We hope to get your real views and opinions, which will be very helpful for our research.
The following content has been approved by the Ethics Committee of School of Design of Hunan University.

▪ Explanation of AVs:
AVs, also known as driverless vehicles, self-driving cars.It uses a driverless system to complete all driving operations, and human drivers can take over.▪ AVs Support Questions: "Please rate your level of support for AVs." ("1 = not support at all" and "100 = strongly support ") ▪ AVs Self-assessed Knowledge Questions: "Please rate your understanding of AVs." ("1 = not understand at all" and "100 = understand very well") "Among the people I know, I can be regarded as an "expert" in the field of AVs." ("1 = strongly disagree" and "100 = strongly agree") "I know how to identify and pick AVs." ("1 = strongly disagree" and "100 = strongly agree") ▪ AVs Objective Knowledge Questions: We arranged 33 trained researchers from the experimental team to conduct respondent recruitment and interviews across China.We paid a fee to researchers and respondents.A total of "I know how to identify and pick AVs." ("1 = strongly disagree" and "100 = strongly agree") ▪ AVs Objective Knowledge Questions: 1 The first batch of real AVs appeared in the 1980s, and then universities and companies successively carried out research and testing of AVs, and in 1995 completed the first autonomous coast-to-coast drive of the United States.In 2017, Waymo announced that it had begun testing AVs, however, there was still an employee in the car.In October 2018, Waymo announced that its test vehicles had traveled in automated mode for over 10,000,000 miles (16,000,000 km).Section Two AVs are vehicles that can sense the environment and drive safely with little or no human intervention.The premise of AVs driving on public roads is to meet the following three conditions: (1) Has a manual override feature that allows a driver to assume control of the AV at any time; (2) Has a driver seated in the control seat of the vehicle while in operation who is prepared to take control of the AV at any moment; (3) Has ability to comply with traffic laws, motor vehicle laws and traffic control devices specified in the driving area.
Modern vehicles provide partly automated features, namely driver assistance technology, but there are still differences between AVs and driver assistance technology.

Section Three
In June 2011, Nevada in the United States became the first jurisdiction in the world to legally operate AVs on public roads.In 2013, the British government allowed testing of AVs on public roads.In 2014, the French government announced that it would allow AVs to be tested on public roads in 2015.Note: Respondents reported their support for AVs, self-assessed knowledge and objective knowledge.Knowledge scores for both Study 3a and Study3b are using pre-experimental data.The effects based on linear regression analysis in SPSS applied to all studies.*P < 0.05, **P < 0.01, ***P < 0.001.
AVs have the same meaning as connected cars, so the two terms are used interchangeably.(True, False, I don't know) 6. Cars can be interconnected without the need for autonomous driving technology.(True, 4.In the minimum degree of automation of AVs, it can complete all driving tasks in any scenario.(True,False,I don't know)5."What is your driving age (calculated from the time you get your driving license)?"Nodriving license, Within 1 year, 1-3 years, 3-5 years, 5-10 years, 10 years or more "What is your main way of commuting?"Walking and cycling, Driving or taking a car (small motor vehicle with less than

Full informational text materials of Study 3a.
. AVs can drive without human control.(True, False, I don't know) 2. AVs are cars with driver assistance technology.(True, False, I don't know) 3.An AV is a car driven by a robot.(True, False, I don't know) 4. In the minimum degree of automation of AVs, it can complete all driving tasks in any scenario.(True, False, I don't know) 5. AVs have the same meaning as connected cars, so the two terms are used interchangeably.(True, False, I don't know) 6. Cars can be interconnected without the need for autonomous driving technology.(True, False, I don't know) 7.An AV can run with different degrees of automation.(True, False, I don't know) 8.The first AV appeared in 1920.(True, False, I don't know) 9. Companies in China have begun testing AVs.(True, False, I don't know) 10.So far, AVs have caused deaths.(True, False, I don't know) "What is your driving age (calculated from the time you get your driving license)?"No driving license, Within 1 year, 1-3 years, 3-5 years, 5-10 years, 10 years or more In the minimum degree of automation of AVs, it can complete all driving tasks in any scenario.(True, False, I don't know) 5. AVs have the same meaning as connected cars, so the two terms are used interchangeably.(True, False, I don't know) 6. Cars can be interconnected without the need for autonomous driving technology.(True, 1. AVs can drive without human control.(True, False, I don't know) 2. AVs are cars with driver assistance technology.(True, False, I don't know) 3.An AV is a car driven by a robot.(True, False, I don't know) 4.
. AVs can drive without human control.(True, False, I don't know) 2. AVs are cars with driver assistance technology.(True, False, I don't know)

Table S1 . Sample details for different studiesTable S1a .
As of 2019, 29 states in the U.S. have passed laws allowing AVs.Demographic characteristic variables of Study 1 respondents

Table S1b .
Demographic characteristic variables of Study 2a respondents

Table S1c .
Demographic characteristic variables of Study 2b respondents Table.S1e Demographic characteristic variables of Study 3b respondents

Table S2 .
Analysis of linear regressions by studiesTableS2a.Effects of self-assessed knowledge on support for AVs.

Table S2b .
Effects of objective knowledge on support for AVs.